In the Dornbusch et al. invention (U.S. patent application 07/636,459 incorporated herein), fixed stations are used in locating one or more portable positioning sensors. Each fixed station produces a set or multiple sets of counter-rotating laser beams which rotate at constant angular velocity. The portable position sensor, which includes a light sensitive detector and computer, can determine its location in reference to the fixed stations, through time measurement of the received laser beams.
It is envisioned that in certain applications it would be useful to maintain processing and display capabilities in a central location. The Dornbusch et al. invention does not provide for this. In addition the Dornbusch et al. invention uses a global frame of reference and requires a number of known site positions in order for the portable position sensor to determine the positions of the fixed referent stations through a calibration sequence.